nico71 Posted January 16 Posted January 16 A 1/30 LEGO Technic replica of an American Heavy Duty Truck with Steering Axle Trailer. Features drive, steering and tri-axle trailer with fixed or steerable axle. Available in different motors configurations (Manual, PFS, Control+) in a single download, all upgradable. Specs : Model inspiration : Western Star and International Truck models Dimensions : 24cm (52.5cm with trailer) x 8.5cm x 11cm Øwheel : 37mm Three versions available : Manual, Power Functions or Control+ Rear wheel drive with a L-motor and differential Small turning radius steering with PFS Servo motor or Control+ L motor, rack and pinion Battery source : PFS+Buwizz 2.0 or PFS+2.4GHz battery or C+ and C+hub or C+ and Buwizz 3.0 On manual version, the steering operated by Hand of God on the top of the cab All versions are included in a single package and are upgradable from and to each version Middle axle with trailing arm suspension to avoid losing traction on uneven ground Tri-Axle Trailer with fixed or automatic steering axle using linkage and a locking pin Landing gear on the trailer with friction gears Openable doors and hood (no fake engine) See in action : Design Process : This model was created for a Truck Exhibition in France to show the possibility of LEGO Trucks in a functional and fun way, either manual or motorized. So I started designing the truck to be the smallest possible with the two motors, that is why I chose the 37mm tire to fit all electronics needed. Plus they have the perfect tire ratio for Heavy Duty Truck looking. Because of the tight space, only the rear axle is powered, and the rack and pinion of the steering is placed in front of the front wheels. Speaking of the steering, I wanted to maximize the turning abilities so I design in a way the range of motion is maximal without colliding with anything, which contributes a lot to the playability. After a few tests, I noticed that the truck could get stuck on small bumps because the central axle was lifted and the rear wheels lost contact with the ground. So I added a rudimentary suspension system in the form of a trailing arms on the central axle, which absorbs bumps that could otherwise cause the rear wheels to lose traction. On the Trailer, I wanted to experiment with steering axle trailer for a while so I was inspired by the Mini Scania R420 and Steering Trailer by TechniMocer which I reused the functioning principle : a lever connected to the saddle operate the trailer axles. Nevertheless, I have improved it with a smaller height for the mechanism, enabling to have the trailer near the rear wheels without any collision. Plus increasing the range of motion of the steering primarily due to extended width. The Truck / Trailer articulation can achieve ±75°. An other functional addition is the locking pin mechanism which enables to choose between two mode of steering for the trailer : fixed or steerable. Simple but effective, as it can be difficult to drive backward the trailer with steering axle mode. For the details, there are quite standard with interior, seats, lights, mirrors and exhausts. The doors can be opened as well as the hood but reveal nothing (no fake engine). The most difficult parts was to reproduce the original form of the cab in a clean look with has many variation in width. For instance the chassis is in 9/11 stud wide, while the cab is only 8 stud, the grill 6 and the mudguard 10, so as you assume there is a lot of half-stud offset inside. I added a minifig inside because I find it funny, even if it is a bit small for the truck (1/43 instead of 1/30). The Rebrickable model do not include it, but the cookie and mug is here ! Instructions are available on my website, as well as rebrickable (3x versions, Manual, PFS and control+), with PDF tutorial for Buwizz and PoweredUp App Profile : 📲 Instructions : https://www.nico71.fr/product/heavy-duty-truck-and-trailer/ 🧩 Bill Of Material : https://rebrickable.com/mocs/MOC-246143/Nico71/heavy-duty-truck-and-steering-axle-trailer/#parts Let me know what do you think about it and if you have questions ! Quote
Timewhatistime Posted January 16 Posted January 16 (edited) This is great! Compact scale, many functions, nice aesthetics. I really like it! If I see it correctly, the trailer's three axles are all steered with the same angle (?) Edited January 16 by Timewhatistime Quote
gyenesvi Posted January 16 Posted January 16 Nice looking mini-scale truck! Nice and simple motorization, and I like that rear steering sytem, elegant solution. Quote
N1K0L4 Posted January 16 Posted January 16 It's amazing, I like the trailer steering solution. There should just about be enough space for HOG gears to go around the steering motor making it a manual and RC model at the same time, am I right? Quote
nico71 Posted January 18 Author Posted January 18 (edited) On 1/16/2026 at 3:36 PM, Timewhatistime said: This is great! Compact scale, many functions, nice aesthetics. I really like it! If I see it correctly, the trailer's three axles are all steered with the same angle (?) Thanks ! The scale is very good for that, a compromise between 1/35 (30mm tire) which is too small and the 1/25 (43mm tire) which is too big. I wanted to create the smallest creation to fit all I need to keep cost low and have maximum playibility regarding available space to play (I like big rig, but they need too much space to drive). That is why I came up with that scale (and because I like the look of the tire). In deed, all trailer axles have the same angle, for simplicity. At start I wanted to try to have different angle but as it is composed of linkage which cross on the center, it was not easy to do it without having a side which turn more than the other (linkage effect as you need to choose a side the operate primarily). I have then looking to different length of the knuckle but as the wheel are close together there is not enough space, or I can limit all the wheel angle to small angle but it doesn't make sense for playability if it is too close of the fixed axle setup. The best is to use rack and pinion with gearing but it create too much backlash and play so suitable for back driving. On 1/16/2026 at 4:43 PM, N1K0L4 said: It's amazing, I like the trailer steering solution. There should just about be enough space for HOG gears to go around the steering motor making it a manual and RC model at the same time, am I right? Thanks ! In fact you can not, first because there is no room for the bevel gearing near the servo (it occupy the whole cabin), secondly because there is also the control+ version, which do not have the same form factor and the cross axle in it, and lastly and more importantly, because you can not operate the servo motor by hand, it is too hard to rotate. So I prefer the approach with or without motor. But the true difficulty was to have the same attachment point or at least the same parts to attach all the various motors, there is only some leftover parts for the hog. A way to use the manual and motorized together is to use a system to disengage the servo motor like a clutch, as I did on my Rally Car V1 in 2013/ Thanks TLCB for the featuring ! Edited January 18 by nico71 Quote
Jeroen Ottens Posted January 20 Posted January 20 Such a clean little truck… and then I read it is motorized! That lifts it up to the next level Quote
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